Update theme support docs

docs/how-to-guides/themes/theme-support.md

@@ -133,19 +133,30 @@ Some colors change dynamically — such as "Primary" and "Secondary" color — s
 
 The colors will be shown in order on the palette, and there's no limit to how many can be specified.
 
-Themes are responsible for creating the classes that apply the colors in different contexts. Core blocks use "color" and "background-color" contexts. So to correctly apply "strong magenta" to all contexts of core blocks a theme should implement the following classes:
+Themes are responsible for creating the classes that apply the colors in different contexts. Core blocks use "color", "background-color", and "border-color" contexts. So to correctly apply "strong magenta" to all contexts of core blocks a theme should implement the classes itself. The class name is built appending 'has-', followed by the class name _using_ kebab case and ending with the context name.
 
 ```css
 .has-strong-magenta-background-color {
-	background-color: #313131;
+	background-color: #a156b4;
 }
 
 .has-strong-magenta-color {
-	color: #f78da7;
+	color: #a156b4;
+}
+
+.has-strong-magenta-border-color {
+	color: #a156b4;
 }
 ```
 
-The class name is built appending 'has-', followed by the class name _using_ kebab case and ending with the context name.
+Starting in WordPress 5.9, to override color values defined by core, themes without a `theme.json` have to set their values via CSS Custom Properties instead of providing the classes. The CSS Custom Properties use the following naming `--wp--preset--color--<slug>`. See more info in [this devnote](https://make.wordpress.org/core/2022/01/08/updates-for-settings-styles-and-theme-json/). For example:
+
+```css
+:root {
+	--wp--preset--color--cyan-bluish-gray: <new_value>;
+	--wp--preset--color--pale-pink: <new_value>;
+}
+```
 
 ### Block Gradient Presets
 
@@ -198,7 +209,16 @@ Themes are responsible for creating the classes that apply the gradients. So to
 }
 ```
 
-### Block Font Sizes:
+Starting in WordPress 5.9, to override gradient values defined by core, themes without a `theme.json` have to set their values via CSS Custom Properties instead of providing the classes. The CSS Custom Properties use the following naming `--wp--preset--gradient--<slug>`. See more info in [this devnote](https://make.wordpress.org/core/2022/01/08/updates-for-settings-styles-and-theme-json/). For example:
+
+```css
+:root {
+	--wp--preset--gradient--vivid-cyan-blue-to-vivid-purple: <new_value>;
+	--wp--preset--gradient--light-green-cyan-to-vivid-green-cyan: <new_value>;
+}
+```
+
+### Block Font Sizes
 
 Blocks may allow the user to configure the font sizes they use, e.g., the paragraph block. The block provides a default set of font sizes, but a theme can overwrite it and provide its own:
 
@@ -244,6 +264,15 @@ As an example for the regular font size, a theme may provide the following class
 <strong>Note:</strong> The slugs `default` and `custom` are reserved and cannot be used by themes.
 </div>
 
+Starting in WordPress 5.9, to override font size values defined by core, themes without a `theme.json` have to set their values via CSS Custom Properties instead of providing the classes. The CSS Custom Properties use the following naming `--wp--preset--font-size--<slug>`. See more info in [this devnote](https://make.wordpress.org/core/2022/01/08/updates-for-settings-styles-and-theme-json/). For example:
+
+```css
+:root {
+	--wp--preset--font-size--small: <new_value>;
+	--wp--preset--font-size--large: <new_value>;
+}
+```
+
 ### Disabling custom font sizes
 
 Themes can disable the ability to set custom font sizes with the following code: